"As someone who was raised a proud Samoan, there is massive appeal in playing for a team that celebrates my heritage, and my culture," he said.
"I have been blessed with so many amazing opportunities over the course of my rugby career, that I feel I can give back to a special community that has always supported me regardless of what colour jersey I was wearing."
Leali'ifano will make the move to New Zealand when he joins the squad for assembly in December.
Leali'ifano has amassed a career total of 171 points with the Australian national side between 2013 and 2019, including a Rugby World Cup campaign.
In recent years, the 34-year-old has been plying his trade in Japan's Top League with Toyota Shokki Shuttles (2018) and NTT Communications (2019 & 2020).
A key playmaker in Brumbies Super Rugby campaigns between 2008 and 2019, Leali'ifano has earned 150 Super Rugby appearances with 963 points to his name.
In 2016, the rugby community was rocked by the news he had been diagnosed with leukaemia. Remarkably, following a successful bone marrow transplant, he returned to Super Rugby in 2017 before heading overseas for a short stint in Ireland's Pro14 and European Rugby Champions Cup with Ulster.
In 2019, his fairytale return to top level rugby was complete when he started at first five in the Wallabies side that put 47 points on the All Blacks in Perth.
That year, he earned his first selection to the Rugby World Cup in Japan, playing in four test matches.